Tire comprising a tread

ABSTRACT

A tire comprises a tread provided with two edges ( 25 A,  25 B) and with a center (C) dividing it into two parts of equal width with sets of blocks ( 21 A,  21 B). Each set of blocks ( 21 A,  21 B) comprises three zones: at the edge ( 211 ), at the center ( 213 ) and intermediate ( 212 ). Each set of blocks ( 21 A,  21 B) comprises a set of chamfers ( 26 A,  26 B,  26 C) which extends over at least the edge zone ( 211 ) and the central zone ( 213 ) of the set of blocks ( 21 A,  21 B). The width LC 1  of the set of chamfers ( 26 A,  26 B,  26 C) over the edge zone ( 211 ) is different from the width LC 2  of the set of chamfers ( 26 A,  26 B,  26 C) over the intermediate zone ( 212 ), the widths LC 1  and LC 2  being comprised between 0.5 mm and 2.5 mm.

TECHNICAL FIELD

The present invention relates to a tyre for a motor vehicle known as an“all-season” tyre. The invention is more particularly suited to a tyreintended to be fitted to a passenger vehicle or van.

PRIOR ART

As is known, a tyre known as an “all-season” tyre is a tyre which offersan excellent compromise between grip on snowy ground/wet ground whilestill maintaining good performance on dry ground. These tyres areintended to run safely all year round, whatever the weather. They havegenerally attained the 3PMSF (3 Peak Mountain Snow Flake) wintercertification attesting to their excellent performance on snowy groundand on wet ground. This certification is notably indicated on one orboth of the sidewalls of this type of tyre.

Document WO2016/134988 discloses an all-season tyre having a treadcomprising two edges and a centre. Said tread is directional andcomprises a plurality of sets of blocks of rubbery material. Each set ofblocks comprises a single block which extends from one edge of the treadto the centre of said tread. More particularly, the block has a centralzone extending overall over an angle β1, said angle β1 being at leastgreater than 35 degrees and at most less than 65 degrees to an axialdirection. The block also has an edge zone extending overall over anangle β3 at least greater than 0 degrees and at most less than 10degrees to said axial direction. Finally, the block has an intermediatezone between the central zone and the edge zone of the block, saidintermediate zone making an angle β2 with said axial direction.

Document WO2019/123277 discloses an all-season tyre comprising aplurality of sets of blocks. Each set of blocks here comprises threeblocks separated by oblique grooves and forming an edge block, a centralblock and an intermediate block between the edge block and the centralblock. Only the edge block here comprises a chamfer positioned on aleading-edge face of this edge block.

There is an ever-present need to improve the performance of all-seasontyres both with regard to the compromise between grip on snowy groundand grip on wet ground and with regard to grip on dry ground.

DISCLOSURE OF THE INVENTION

The present invention seeks to at least partially meet this need.

More specifically, the present invention seeks to improve the compromisebetween grip on snowy ground/wet ground for an all-season tyre while atthe same time improving the performance in terms of grip on dry ground.

The invention relates to a tyre comprising a tread.

A “tyre” means all types of tyre casing made of a rubbery material andwhich, during running is subjected to an internal pressure or notsubjected to such an internal pressure during running (which is the caseof an airless tyre casing without compressed air, for example of theTweel™ type).

More particularly, the invention relates to a tyre comprising adirectional tread of width W.

The tread comprises two edges and a centre C. The edges delimitboundaries between this tread and two sidewalls. The centre C dividesthe tread into two parts of substantially equal width. The tread, on oneof its two parts, comprises a plurality of sets of blocks succeeding oneanother in a circumferential direction.

What is meant by a “circumferential direction” is a direction that istangential to any circle centred on the axis of rotation. This directionis perpendicular both to an axial direction and to a radial direction.

What is meant by an “axial direction” is a direction parallel to theaxis of rotation of the tyre.

What is meant by a “radial direction” is a direction which isperpendicular to the axis of rotation of the tyre (this directioncorresponds to the direction of the thickness of the tread at the centreof said tread).

Each set of blocks comprises at least one block. What is meant by a“block” is a raised element delimited by grooves and comprising lateralwalls and a contact face, the latter being intended to come into contactwith the ground during running. In instances in which the set of blockscomprises just one single block, said set of blocks and said block aremerged.

What is meant by a “groove” is a void for which the distance between thewalls of material that delimit said groove is greater than 2 mm and ofwhich the depth is greater than or equal to 1 mm.

What is meant by a “sipe” is a void for which the distance between thewalls of material that delimit said sipe is less than or equal to 2 mmand of which the depth is greater than or equal to 1 mm.

Each set of blocks extends from one of the edges of the tread towardsthe centre of said tread with a certain non-zero curvature. The blocksets curved in this way define the directional nature of the tread.

Each set of blocks comprises an edge zone near an edge of the tread, acentral zone near the centre of said tread and an intermediate zonebetween the central zone and the edge zone. Each set of blocks comprisesa set of chamfers comprising at least one chamfer, said set of chamfersextending at least over the edge zone and the central zone of the set ofblocks.

What is meant by a “set of chamfers” is a set comprising one or morechamfers, the chamfer(s) extending over the one same lateral face of theset of blocks. If the set of blocks comprises just one single block, theset of chamfers then comprises one single chamfer extending over alateral face of the block. If the set of blocks comprises severalblocks, the set of chamfers comprises at least two chamfers extendingover two lateral faces of two blocks. These lateral faces belong to thesame lateral face of the set of blocks, which is to say that they aresituated on the same side of the set of blocks.

What is meant by a “chamfer” is an inclined wall which extends from thetread surface of the tread towards the bottom of the groove delimitingthe wall. The inclination of the wall is such that the block widenstowards the bottom of this groove. Each chamfer has a chamfer height anda chamfer width. The chamfer height corresponds to the distance betweenthe tread surface of the tread and the radially innermost point of thechamfer in the groove. This distance is measured in the radialdirection. The chamfer width corresponds to the distance between theradially outermost point of the chamfer and the radially innermost pointof this chamfer in the groove, projected onto the tread surface of thetread. This distance is measured in the circumferential direction.

What is meant by a “tread surface” of a tread is the surface that groupstogether all the points of the tyre that will come into contact with theground under normal running conditions. These points that will come intocontact with the ground belong to the contact faces of the blocks. For atyre, the “normal running conditions” are the use conditions defined bythe ETRTO (European Tyre and Rim Technical Organisation) standard. Theseuse conditions specify the reference inflation pressure corresponding tothe load-bearing capacity of the tyre as indicated by its load index andits speed rating. These use conditions can also be referred to as“nominal conditions” or “working conditions”.

The width of the set of chamfers over the edge zone is different fromthe width of the set of chamfers over the intermediate zone, said widthsbeing comprised between 0.5 mm and 2.5 mm.

The chamfer locally improves the stiffness of the set of blocks makingit possible to improve the grip of this tyre on dry ground. This grip isparticularly improved on the edge zone of the set of blocks whichextends chiefly in the axial direction. The edge zone, the intermediatezone and the central zone of the set of blocks extend in differentdirections. Furthermore, these zones may have different widths. Byincreasing those zones of the set of blocks that enjoy the benefit of achamfer and by adapting the width of this chamfer according to the localwidth of the set of blocks and/or according to the direction in whichthis set of blocks locally extends, the grip of the tyre on dry groundis optimized.

As a preference, the width of the set of chamfers over the intermediatezone is greater than the width of the set of chamfers over the edgezone.

As a preference, the difference in width of the set of chamfers betweenthe intermediate zone and the edge zone is at least 0.3 mm.

As a preference, the set of chamfers extends in the central zone of theset of blocks with a predetermined width.

As a preference, the width of the set of chamfers in the intermediatezone is greater than the width of the set of chamfers in the edge zoneand than the width of the set of chamfers in the central zone.

As a preference, the set of blocks comprises a leading-edge face and atrailing-edge face, and said set of chamfers extends at the leading-edgeface of said set of blocks.

What is meant by the “leading-edge face” of the set of blocks is theface of said set of blocks that is first to enter the contact patch, inthe preferred direction of running of the tyre. The leading-edge face ofthe set of blocks extends only on the one same side of the set ofblocks. Thus, if the set of blocks comprises just one block, theleading-edge face of the set of blocks extends over a lateral wall ofthis block. If the set of blocks comprises several blocks, theleading-edge face of the set of blocks extends over several lateralwalls of different blocks.

What is meant by the “trailing-edge face” of the set of blocks is theface of said set of blocks that is last to leave the contact patch, inthe preferred direction of running of the tyre. The trailing-edge faceof the set of blocks extends only on the one same side of the set ofblocks. Thus, if the set of blocks comprises just one block, thetrailing-edge face of the set of blocks extends over a lateral wall ofthis block. If the set of blocks comprises several blocks, thetrailing-edge face of the set of blocks extends over several lateralwalls of different blocks.

As a preference, the set of blocks comprises another set of chamfersextending at the trailing-edge face of said set of blocks.

As a preference, the set of blocks comprises a sipe extending along thelength of the set of blocks, said sipe being at least partiallychamfered.

In another embodiment of the invention, the set of blocks comprises atleast three blocks, a first block referred to as an edge block near theedge of the tread, a second block referred to as a central block nearthe central zone, and a third block referred to as an intermediate blockpositioned between the edge block and the central block, and wherein theset of blocks comprises a set of chamfers comprising at least threechamfers, a first chamfer referred to as an edge chamfer of width,extending in the edge block, a second chamfer referred to as a centralchamfer, extending in the central block, a third chamfer referred to asan intermediate chamfer, extending in the intermediate block. The widthof the edge chamfer is different from the width of the intermediatechamfer, and the width of the central chamfer is different from thewidth of the intermediate chamfer, said widths being comprised between0.5 mm and 2.5 mm. The width of the set of chamfers in the intermediatezone is greater than the width of the set of chamfers in the edge zoneand also greater than the width of the set of chamfers in the centralzone.

The composition of the rubbery material of the blocks has a glasstransition temperature Tg comprised between −40° C. and −10° C. andpreferably between −35° C. and −15° C. and a complex dynamic shearmodulus G* measured at 60° C. comprised between 0.5 MPa and 2 MPa, andpreferably between 0.7 MPa and 1.5 MPa.

A conventional physical characteristic of an elastomeric compound is itsglass transition temperature Tg, the temperature at which theelastomeric compound passes from a deformable rubbery state to a rigidglassy state. The glass transition temperature Tg of an elastomericcompound is generally determined during the measurement of the dynamicproperties of the elastomeric compound, on a viscosity analyser(Metravib VA4000), according to the standard ASTM D 5992-96. The dynamicproperties are measured on a sample of vulcanized elastomeric compound,that is to say elastomeric compound that has been cured to a degree ofconversion of at least 90%, the sample having the form of a cylindricaltest specimen having a thickness equal to 2 mm and a cross-sectionalarea equal to 78.5 mm². The response of the sample of elastomericcompound to a simple alternating sinusoidal shear stress, having apeak-to-peak amplitude equal to 0.7 MPa and a frequency equal to 10 Hz,is recorded. A temperature sweep is carried out at a constant rate ofrise in temperature of +1.5° C./min. The results utilized are generallythe complex dynamic shear modulus G*, comprising an elastic part G′ anda viscous part G″, and the dynamic loss tgδ, equal to the ratio G″/G′.The glass transition temperature Tg is the temperature at which thedynamic loss tgδ reaches a maximum during the temperature sweep. Thevalue of G* measured at 60° C. is indicative of the stiffness of therubbery material, namely of its resistance to elastic deformation.

This composition of the rubbery material makes it possible to improveperformance in terms of grip on snowy/wet ground. Because this materialis less stiff overall, the set of chamfers on the set of blocks makes itpossible to locally stiffen the stiffness of the set of blocks and thisnotably improves the performance in terms of grip on dry ground. Thebalance of performance between snowy/wet ground and dry ground is thusoptimized.

The tyre has a 3PMSF winter certification, said certification beingindicated on a sidewall of this tyre.

The present invention will be understood better upon reading thedetailed description of embodiments that are given by way of entirelynon-limiting examples and are illustrated by the appended drawings, inwhich:

FIG. 1 is a schematic perspective view of a tyre according to the priorart;

FIG. 2 is a schematic perspective view of a partial cross section of atyre according to another prior art;

FIG. 3 is a detailed partial view of a tread, when new, of a tyreaccording to a first embodiment of the invention;

FIG. 4 is an enlarged view of a set of blocks of the tread of FIG. 3 ;

FIG. 5 is a view in cross section of the block of FIG. 4 , on a plane ofsection A-A;

FIG. 6 is a view in cross section of the block of FIG. 4 , on a plane ofsection B-B;

FIG. 7 is a view in cross section of the block of FIG. 4 , on a plane ofsection C-C;

FIG. 8 is a detailed partial view of a tread, when new, of a tyreaccording to a second embodiment of the invention.

The invention is not limited to the embodiments and variants presentedand other embodiments and variants will become clearly apparent to aperson skilled in the art.

In the various figures, identical or similar elements bear the samereferences.

FIG. 1 schematically depicts a tyre 10 according to the prior art. Thistyre 10 comprises a tread 20 and two sidewalls 30A, 30B (of which justone is depicted here), said tread 20 and said sidewalls 30A, 30Bcovering a carcass 40 (which is not depicted in FIG. 1 ). FIG. 2 moreparticularly details the carcass 40 of a tyre 10 according to the priorart. This carcass 40 thus comprises a carcass reinforcement 41 made upof threads 42 coated with rubber composition, and two beads 43 eachcomprising annular reinforcing structures 44 (in this instance beadwires) which hold the tyre 10 on a rim (the rim is not depicted). Thecarcass reinforcement 41 is anchored in each of the beads 43. Thecarcass 40 additionally comprises a crown reinforcement comprising twoworking plies 44 and 45. Each of the working plies 44 and 45 isreinforced by filamentary reinforcing elements 46 and 47 which areparallel within each layer and crossed from one layer to the other,making angles comprised between 10° and 70° with the circumferentialdirection X.

The tyre further comprises a hoop reinforcement 48 arranged radially onthe outside of the crown reinforcement. This hoop reinforcement 48 isformed of reinforcing elements 49 that are oriented circumferentiallyand wound in a spiral. The tyre 10 depicted in FIG. 2 is a “tubeless”tyre. It comprises an “inner liner” made of a rubber compositionimpervious to the inflation gas, covering the interior surface of thetyre.

FIG. 3 is a detailed partial view of a tread 20 according to theinvention. The tread 20 here is as new. This tread 20 comprises twotread parts 20A, 20B of substantially equal width W/2. Each tread part20A, 20B respectively comprises a plurality of sets of blocks 21A, 21B.The sets of blocks succeed one another in a circumferential direction.More particularly, one set of blocks belongs to a pattern M of pitch P.This pattern M is repeated n times on the circumference of the tyre.This repeat may be an “iso-dimensional” repeat. The tread is then saidto be monopitch. As an alternative, this repeat may occur with differentmagnification factors. The tread is then said to be multipitch.

Each set of blocks 21A, 21B extends respectively from one of the edges25A, 25B of the tread 20 as far as the central axis C with a non-zerocurvature. The central axis C thus comprises an alternation of blocks21A, 21B originating respectively from the edges 25A, 25B of the tread20. The tread 20 here is said to be directional, which means to say thatthe blocks 21A, 21B are specifically arranged to optimize thebehavioural characteristics of the tyre depending on a predeterminedsense of rotation. This sense of rotation is conventionally indicated byan arrow on the sidewall of the tyre (arrow labelled R in FIG. 3 ).

In the embodiment of FIG. 3 , each set of blocks 21A, 21B comprises asingle block. As an alternative, the set of blocks may comprise a numberof blocks greater than or equal to 2. In each set of blocks, the blocksare then separated by at least one groove. This groove extends in anaxial direction or in an oblique direction having both a non-zerocomponent in the circumferential direction and a non-zero component inthe axial direction.

It will be noted that the blocks have a maximum height at least equal to5.5 mm and at most equal to 9 mm. As a preference, the maximum height ofthe blocks is at most equal to 7.5 mm. This maximum height is measuredfor the blocks at the central axis C. It corresponds to the distancebetween a tread surface 23 of the tread and a bottom surface 24. Themaximum height of a block corresponds to the maximum depth of thegrooves delimiting this block.

What is meant by a “tread surface” 23 of a tread 20 is the surface thatgroups together all the points of the tyre that will come into contactwith the ground under normal running conditions. These points that willcome into contact with the ground belong to the contact faces of theblocks. For a tyre, the “normal running conditions” are the useconditions defined by the ETRTO (European Tyre and Rim TechnicalOrganisation) standard. These use conditions specify the referenceinflation pressure corresponding to the load-bearing capacity of thetyre as indicated by its load index and its speed rating. These useconditions can also be referred to as “nominal conditions” or “workingconditions”.

What is meant by “bottom surface” 24 is a theoretical surface passingthrough the radially interior points of the grooves of the tread 20. Itthus delimits the boundary between the tread 20 and the carcass 40 ofthe tyre. This bottom surface 24 extends between a first edge 25A and asecond edge 25B of the tread 20.

Remember that what is meant by an “edge” 25A, 25B of the tread 20 is therespective boundaries between the tread 20 and the sidewalls 30A, 30B.These two edges 25A, 25B are distant from one another by the value Wcorresponding to the width of the tread 20. These two edges 25A, 25B aresituated at equal distances from the central axis C.

It will also be noted that a winter certification 3PMSF is marked on atleast one of the sidewalls 30A, 30B of the tyre.

FIG. 4 is an enlarged view of the set of blocks 21A of FIG. 3 . This setof blocks 21A is delimited by a contact surface 23, a bottom surface 24and lateral faces 26, 27, 28. Among these lateral faces, a distinctionis made between a leading-edge face 26, a trailing-edge face 27 and acentral face 28. The contact surface 23, the bottom surface 24, theleading-edge face 26, the trailing-edge face 27, the central face 28 andthe edge 25A delimit the total volume VT of rubbery material containedin the set of blocks 21A.

One method for determining the total volume VT of rubbery materialcontained in the set of blocks 21A would be to make full use of thecapabilities of 3-D scanners able to directly digitize the volume of acomplex object. An example of such a scanner is, for example, the WOLF &BECK TMM-570 metrology machine that employs a laser probe.

The set of blocks 21A here is divided chiefly into three zones,comprising an edge zone 211, an intermediate zone 212 extending the edgepart 211, a central zone 213 extending the intermediate zone 212. Eachof the zones of the set of blocks 21A here has a main direction ofextension specific to it. Thus, the edge zone 211 mainly extends overallparallel to the axial direction Y. The central zone 213 is steeplyinclined with respect to the axial direction Y and the intermediate zone212 has an inclination that is comprised between the inclination of theedge zone 211 and the inclination of the central zone 213. The set ofblocks 21A therefore exhibits a non-zero overall curvature.

Each set of blocks 21A comprises a set of chamfers 26A, 26B, 26C. Thisset of chamfers here comprises an edge chamfer 26A extending over theedge zone 211, an intermediate chamfer 26B extending over theintermediate zone 212, and a central chamfer 26C extending over thecentral zone 213. The edge chamfer 26A, the intermediate chamfer 26B andthe central chamfer 26C follow-on from one another in the axialdirection and extend over the leading-edge face of the set of blocks.The edge chamfer 26A, the intermediate chamfer 26B and the centralchamfer 26C have respective widths LC1, LC2, LC3. What is meant by thewidth of the chamfer is the mean width of this chamfer in the selectedzone of the set of blocks. These widths LC1, LC2, LC3 are comprisedbetween 0.5 mm and 2.5 mm.

FIG. 5 illustrates a view in cross section of the set of blocks 21A ofFIG. 4 , on a plane of section A-A in the edge zone 211 at the edgechamfer 26A. The edge chamfer 26A forms an inclined plane which extendsbetween a first point A and a second point B. The first point Acorresponds to the intersection between the edge chamfer 26A and thetread surface 23 of the tread. The second point B corresponds to theintersection between the edge chamfer 26A and a lateral wall delimitingthe edge zone 211. The edge chamfer 26A is defined by a height, a widthand by an angle of inclination measured with respect to thecircumferential direction X. The height of the edge chamfer 26Acorresponds to the distance between the first point A and the secondpoint B in a radial projection, which is to say in a projection onto theaxis Z. The height of the edge chamfer 26A here is comprised between 0.5and 1 mm. The width LC1 of the edge chamfer 26A corresponds to thedistance between the first point A and the second point B in acircumferential projection, which is to say in a projection onto theaxis X. As already indicated, the width LC1 of the edge chamfer 26A hereis comprised between 1.5 and 2 mm. The angle of inclination of the edgechamfer 26A is comprised between 30 degrees and 50 degrees with respectto the circumferential direction X.

FIG. 6 illustrates a view in cross section of the set of blocks 21A ofFIG. 4 , on a plane of section B-B in the intermediate zone 212 at theintermediate chamfer 26B. The intermediate chamfer 26B forms an inclinedplane which extends between a first point A′ and a second point B′. Thefirst point A′ corresponds to the intersection between the intermediatechamfer 26B and the tread surface 23 of the tread. The second point B′corresponds to the intersection between the intermediate chamfer 26B anda lateral wall delimiting the intermediate zone 212. The intermediatechamfer 26B is defined by a height, a width and by an angle ofinclination measured with respect to the circumferential direction X.The height of the intermediate chamfer 26B corresponds to the distancebetween the first point A′ and the second point B′ in a radialprojection, which is to say in a projection onto the axis Z. The heightof the intermediate chamfer 26B here is comprised between 0.5 and 1 mm.The width LC2 of the intermediate chamfer 26B corresponds to thedistance between the first point A′ and the second point B′ in acircumferential projection, which is to say in a projection onto theaxis X. As already indicated, the width LC2 of the intermediate chamfer26B here is comprised between 1.5 and 2 mm. The angle of inclination ofthe intermediate chamfer 26B is comprised between 30 degrees and 50degrees with respect to the circumferential direction X.

FIG. 7 illustrates a view in cross section of the set of blocks 21A ofFIG. 4 , on a plane of section C-C in the central zone 213 at thecentral chamfer 26C. The central chamfer 26C forms an inclined planewhich extends between a first point A″ and a second point B″. The firstpoint A″ corresponds to the intersection between the central chamfer 26Cand the tread surface 23 of the tread. The second point B″ correspondsto the intersection between the central chamfer 26C and a lateral walldelimiting the central zone 213. The central chamfer 26C is defined by aheight, a width and by an angle of inclination measured with respect tothe circumferential direction X. The height of the central chamfer 26Ccorresponds to the distance between the first point A″ and the secondpoint B″ in a radial projection, which is to say in a projection ontothe axis Z. The height of the central chamfer 26C here is comprisedbetween 0.5 and 1 mm. The width LC3 of the central chamfer 26Ccorresponds to the distance between the first point A″ and the secondpoint B″ in a circumferential projection, which is to say in aprojection onto the axis X. As already indicated, the width LC3 of thecentral chamfer 26C here is comprised between 1.5 and 2 mm. The angle ofinclination of the central chamfer 26C is comprised between 30 degreesand 50 degrees with respect to the circumferential direction X.

As a preference, the width LC2 of the intermediate chamfer 26B over theintermediate zone 212 is different from the width LC1 of the edgechamfer 26A over the edge zone 211. Advantageously, the difference inwidth LC2-LC1 of the set of chamfers between the intermediate zone 212and the edge zone 211 is at least 0.3 mm.

In the embodiment illustrated in FIGS. 5 to 7 , the width LC2 of theintermediate chamfer 26B is greater than the width LC1 of the edgechamfer 26A in the edge zone 211 and than the width LC3 of the centralchamfer 26C in the central zone 213.

In FIG. 4 , the edge chamfer 26A, the intermediate chamfer 26B and thecentral chamfer 26C extend at a leading-edge face of the set of blocks21A. Said set of blocks 21A also comprises a trailing-edge face. Anotherset of chamfers extends over said trailing-edge face. As a preference,the other set of chamfers has a width that is constant over the set ofblocks 21A.

In FIG. 4 , the set of blocks 21A comprises a sipe 29 extending alongthe length of said set of blocks 21A. As a preference, the sipe 29 is atleast partially chamfered.

FIG. 8 illustrates a second embodiment in which the set of blocks 21Acomprises three blocks 211A, 212A, 213A. The first block 211A, referredto as an edge block, is positioned near the edge 25A of the tread. Asecond block 212A, referred to as an intermediate block, is positionedin the continuation of the edge block 211A. A third block 213A, referredto as a central block, is positioned in the continuation of theintermediate block 212A. The intermediate block 212A is thereforepositioned between the edge block 211A and the central block 213A. Theedge block 211A is separated from the intermediate block 212A by a firstgroove 221. The intermediate block 212A is separated from the centralblock 213A by a second groove 222. The first groove 221 and the secondgroove 222 here extend mainly in an oblique direction. This obliquedirection has both a component in the circumferential direction X and acomponent in the axial direction Y. As an alternative, the first groove221 and/or the second groove 222 extends (extend) only in thecircumferential direction X. In addition, the edge block 211A herecomprises an edge chamfer 26A of width LC1. The intermediate block 212Acomprises an intermediate chamfer 26B of width LC2. The central block213A comprises a central chamfer 26C of width LC3.

The width LC1 of the edge chamfer is different from the width LC2 of theintermediate chamfer and the width LC3 of the central chamfer isdifferent from the width LC2 of the intermediate chamfer. The widthsLC1, LC2, LC3 are comprised between 0.5 mm and 2.5 mm, and the width LC2of the set of chamfers in the intermediate zone is greater than thewidth LC1 of the set of chamfers in the edge zone and than the width LC3of the set of chamfers in the central zone.

For the embodiment illustrated in FIGS. 1 to 8 , each set of blocks 21Ais formed from a rubbery material. In one preferred embodiment, thecomposition of this rubbery material has a glass transition temperaturecomprised between −40° C. and −10° C. and preferably between −35° C. and−15° C. and a shear modulus measured at 60° C. comprised between 0.5 MPaand 2 MPa, and preferably between 0.7 MPa and 1.5 MPa.

In one preferred embodiment, the composition of the rubbery material ofthe sets of blocks is based on at least:

-   -   an elastomer matrix comprising more than 50% by weight of a        solution SBR bearing a silanol functional group and an amine        functional group;    -   20 to 200 phr of at least one silica;    -   a coupling agent for coupling the silica to the solution SBR,    -   10 to 100 phr of a hydrocarbon-based resin having a Tg of        greater than 20° C.;    -   15 to 50 phr of a liquid plasticizer.

The solution SBR in this preferred embodiment is a copolymer ofbutadiene and styrene, prepared in solution. The characteristic featurethereof is that it bears a silanol functional group and an aminefunctional group. The silanol functional group of the solution SBRbearing a silanol functional group and an amine functional group may forexample be introduced by hydrosilylation of the elastomer chain by asilane bearing an alkoxysilane group, followed by hydrolysis of thealkoxysilane functional group to give a silanol functional group. Thesilanol functional group of the solution SBR bearing a silanolfunctional group and an amine functional group may equally be introducedby reaction of the living elastomer chains with a cyclic polysiloxanecompound as described in EP 0 778 311. The amine functional group of thesolution SBR bearing a silanol functional group and an amine functionalgroup may for example be introduced by initiating polymerization usingan initiator bearing such a functional group. A solution SBR bearing asilanol functional group and an amine functional group may equally beprepared by reacting the living elastomer chains with a compound bearingan alkoxysilane functional group and an amine functional group accordingto the procedure described in patent application EP 2 285 852, followedby hydrolysis of the alkoxysilane functional group to give a silanolfunctional group. According to this preparation procedure, the silanolfunctional group and the amine functional group are preferably situatedwithin the chain of the solution SBR, not including the ends of thechain. The reaction producing the hydrolysis of the alkoxysilanefunctional group borne by the solution SBR to give a silanol functionalgroup may be carried out according to the procedure described in patentapplication EP 2 266 819 A1 or else by a step of stripping the solutioncontaining the solution SBR. The amine functional group can be aprimary, secondary or tertiary amine functional group, preferably atertiary amine functional group.

The invention is not limited to the embodiments and variants presentedand other embodiments and variants will become clearly apparent to aperson skilled in the art.

1.-11. (canceled)
 12. A tire comprising a directional tread (20), thetread (20) comprising two edges (25A, 25B) and a center (C) dividing thetread into two parts of substantially equal width, the tread (20)comprising, on one of the two parts of the tread, a plurality of sets ofblocks (21A, 21B), each set of blocks (21A, 21B) comprising at least oneblock, each set of blocks (21A, 21B) extending from one of the edges(25A, 25B) of the tread toward the center (C) of the tread (20) with anon-zero curvature, each set of blocks (21A) comprising an edge zone(211) near an edge of the tread, a central zone (213) near the center ofthe tread, and an intermediate zone (212) between the edge zone (211)and the central zone (213), each set of blocks (21A) comprising a set ofchamfers (26A, 26B, 26C) comprising at least one chamfer, the set ofchamfers (26A, 26B, 26C) extending over the edge zone (211), the centralzone (213) and the intermediate zone (212) of the set of blocks (21A),wherein a width LC1 of the set of chamfers (26A, 26B, 26C) over the edgezone (211) is different from a width LC2 of the set of chamfers (26A,26B, 26C) over the intermediate zone (212), wherein the widths LC1 andLC2 are between 0.5 mm and 2.5 mm, a width of a chamfer corresponding toa distance between a radially outermost point of the chamfer and aradially innermost point of the chamfer in the groove, projected onto atread surface of the tread, measured in a circumferential direction. 13.The tire according to claim 12, wherein the width LC2 of the set ofchamfers (26A, 26B, 26C) over the intermediate zone (212) is greaterthan the width LC1 of the set of chamfers over the edge zone (211). 14.The tire according to claim 12, wherein a difference in width LC2-LC1 ofthe set of chamfers (26A, 26B, 26C) between the intermediate zone (212)and the edge zone (211) is at least 0.3 mm.
 15. The tire according toclaim 12, wherein the set of chamfers (26A, 26B, 26C) extends in thecentral zone (213) of the set of blocks (21A) with a width LC3.
 16. Thetire according to claim 15, wherein the width LC2 of the set of chamfers(26A, 26B, 26C) in the intermediate zone (212) is greater than the widthLC1 of the set of chamfers in the edge zone (211) and than the width LC3of the set of chamfers (26A, 26B, 26C) in the central zone (213). 17.The tire according to claim 12, the set of blocks comprising aleading-edge face (26) and a trailing-edge face (27), wherein the set ofchamfers (26A, 26B, 26C) extends at the leading-edge face of the set ofblocks (21A).
 18. The tire according to claim 17, wherein the set ofblocks (21A) comprises another set of chamfers extending at thetrailing-edge face of the set of blocks (21A).
 19. The tire according toclaim 12, wherein the set of blocks (21A) comprises a sipe (29)extending along a length of the set of blocks (21A), the sipe (29) beingat least partially chamfered.
 20. The tire according to claim 12,wherein the set of blocks (21A) comprises at least three blocks (211A,212A, 213A), a first block (211A) referred to as an edge block near anedge (25A) of the tread, a third block (213A) referred to as a centralblock near the central zone, and a second block (212A) referred to as anintermediate block positioned between the edge block (211A) and thecentral block (213A), wherein the set of blocks (211A, 212A, 213A)comprises a set of chamfers (26A, 26B, 26C) comprising at least threechamfers, a first chamfer referred to as an edge chamfer (26A) of widthLC1, extending in the edge block, a second chamfer referred to as anintermediate chamfer (26B) of width LC2, extending in the intermediateblock (26B), a third chamfer (26C), referred to as a central chamfer, ofwidth LC3, extending in the central block (26C), the width LC1 of theedge chamfer (26A) being different from the width LC2 of theintermediate chamfer (26B), and the width LC3 of the central chamfer(26C) being different from the width LC2 of the intermediate chamfer(26B), the widths LC1, LC2, LC3 being comprised between 0.5 mm and 2.5mm, and wherein the width LC2 of the set of chamfers (26B) in theintermediate zone (212A) is greater than the width LC1 of the set ofchamfers (26A) in the edge zone (211A) and than the width LC3 of the setof chamfers (26C) in the central zone (213A).
 21. The tire according toclaim 12, wherein a composition of the rubbery material of the blockshas a glass transition temperature Tg comprised between −40° C. and −10°C. and a complex dynamic shear modulus G* comprised between 0.5 MPa and2 MPa, the measurements being taken at a temperature of 60° C. undersimple alternating sinusoidal shear stress with a peak-to-peak amplitudeequal to 0.7 MPa and a frequency equal to 10 Hz.
 22. The tire accordingto claim 12, wherein the tire (10) has a 3PMSF winter certification, thecertification being indicated on a sidewall (30A) of the tire.